1. Field of the Invention
The present invention relates generally to a keypad, and more particularly, to an illuminated keypad capable of being used under a condition of poor light, such as at night.
2. The Related Art
A Keypad is widespread and used in various electronic devices, such as a mobile phone, a computer, a PDA (Personal Digital Assistant), etc. Under a condition of poor light, such as at night, it is also required that the keypad is conveniently recognized. So a keypad with illumination function is manufactured and is commonly used nowadays.
A traditional illuminated keypad of an electronic device has a baseboard. A plurality of keys arranged in array is integrally protruded from a top surface of the baseboard. A top surface of each key is a translucent layer and is manufactured by a silk-screen printing technique or Plastic Laser Etching. So light can be received by the translucent layers of the keys for illuminating. Each of the keys extends a projection portion downward to control a switch on a printed circuit board disposed under the baseboard. When assembling, the illuminated keypad is fixed to the printed circuit board of the electronic device, and a plurality of light-emitting components, such as LEDs, or LCDs, are positioned on the printed circuit board. The light-emitting components emit light to the translucent layers of the keys so as to provide enough light for users to distinguish alphanumeric characters printed on the keys.
However, because the light from the light-emitting components is transmitted and scattered in the air, some energy of the light is dissipated in the air and results in inadequate illumination of the keypads, which in turn results in difficulty to recognize the alphanumeric characters printed on the keys.
In order to solve the above questions, there discloses another improved illuminated keypad having a light guide plate. The light guide plate is disposed under the baseboard of the keypad, and the projection portions of the keys penetrate the light guide board. The light guide plate is made of substantially light conducting material. A plurality of light-emitting components is disposed inside the light guide plate. Light emitted from the light-emitting components is reflected by many times inside the light guide plate, and then is transmitted to the top surface of the keys, so the keys are illuminated for users distinguishing the alphanumeric characters printed on the keys.
However, it is disadvantage of the improved illuminated keyboard with a light guide plate. Because the light is transmitted inside a large space of the light guide plate and reflected by the light guide plate for many times before being transmitted to the keys, some energy of the light is also dissipated in the course of transmitting and reflection. This results in lower efficiency of light energy utilization. Additionally, the large area of the total light guide plate increases manufacturing cost.